The placenta consists of vascular tissue in which oxygen and nutrients can pass from the mother’s blood into that of the fetus, and waste products can pass in the reverse direction. The placenta is expelled from the uterus at the birth of the fetus, when it is often called the afterbirth. Marsupials and monotremes do not develop placentas

2 Botany (In flowers) part of the ovary wall to which the ovules are attached.